Method for producing borazine compound

ABSTRACT

In a synthesis of a borazine compound by a reaction of an alkali boron hydride represented by ABH 4  (A represents lithium atom, sodium atom or potassium atom) and an amine salt represented by (RNH 3 ) n X (R represents a hydrogen atom or an alkyl group, X represents a sulfate group or a halogen atom, and n is 1 or 2), or b) diborane (B 2 H 6 ) and an amine represented by RNH 2  (R represents a hydrogen atom or an alkyl group), a water content of raw material is controlled below a prescribed value; mixed solvents containing solvents each having a prescribed boiling point are used as a solvent for reaction; or a raw material is gradually fed to a reactor in a reaction. Or, a borazine compound is subjected to distillation purification treatment and filtration treatment. By such a method, a high purity of borazine compound can be produced safely and in a high yield.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for producing borazinecompounds. Borazine compounds are used to form, for example, aninterlayer dielectric film for semiconductor, a barrier metal layer andan etching stopper layer.

2. Description of Related Art

With higher functionalization of information devices, design rule of LSIhas been required to be finer year by year. In production of LSI withfiner design rule, materials composing LSI should also have higherperformance and fulfill function even on fine LSI.

For example, as for materials used for an interlayer dielectric film inLSI, high dielectric constant causes signal delay. In fine LSI, effectsof the signal delay is particularly significant. Therefore, developmentof a new low dielectric material which can be used for an interlayerdielectric film has been needed. Also, it is necessary not only to havelow dielectric constant but also superior characteristics such ashumidity resistance, heat resistance, mechanical strength, etc. to beused as an interlayer dielectric film.

As a material to respond to these requirements, a compound havingborazine ring backbone has been proposed (for example, see US Laid OpenPatent No. 2002-58142). A compound having borazine ring backbone(borazine compound) has small molecular polarizability and thus a coatedfilm formed provides low dielectric constant. Moreover, the coated filmformed is superior in heat resistance.

As a borazine compound, N-alkylborazine in which a nitrogen atomconstructing the borazine rings is bonded with an alkyl group.N-alkylborazine in itself is used for a raw material to form aninterlayer dielectric film for semiconductor and the like. Further,N-alkylborazine is also used as an intermediate compound in producingother borazine compounds. For example, hexaalkylborazine is produced bysubstituting a hydrogen atom bonded to a boron atom in a borazinecompound with an alkyl group.

As a technique for producing a borazine compound, 1) a techniquereacting an alkali boron hydride (for example, sodium boron hydride(NaBH₄)) and an amine salt (for example, methylamine hydrochloride(CH₃NH₃Cl)) in a solvent; 2) a technique reacting diborane (B₂H₆) and anamine compound (for example, methylamine (CH₃NH₂)) in a solvent; areknown.

BRIEF SUMMARY OF THE INVENTION

The present inventors have, after analyzing in detail borazine compoundsobtained by the synthetic techniques, found that the borazine compoundscontains various impurities, which cause lowering of a purity of thedesired borazine compound. Specifically, in addition to a compound whichis thought to be a decomposed matter of borazine compound (for example,amine and boric acid) and a boron ether compound which is formed by atrace component in a solvent, in a synthesis of a N-alkylborazinecompound, N-alkylcycloborazane of a by-product can be contained as animpurity. In view of application to precision apparatus such as aninterlayer dielectric film, a content of these compounds contained asimpurities is desirably lowered to a level as low as possible. Further,formation of N-alkylcycloborazane as a by-product in a synthesis of aborazine compound arises another problem. Namely, as synthesis of aborazine compound proceeds, N-alkylcycloborazane having a sublimationproperty deposits in a cooling section of synthesis apparatus. Furtherprogression of deposition of N-alkylcycloborazane could lead, in someinstances, to blockage of a cooling section to make continuation ofsynthesis impossible. Furthermore, safety could be impaired due to riseof pressure in a synthesis apparatus. Even when the deposition isremoved before blocking a cooling section, stoppage of synthesis isneeded regularly, leading to lowering of synthesis efficiency. For apurpose of reference, structures of N-alkylborazine, boron ethercompound and N-alkylcycloborazane are shown below:

wherein R represents an alkyl group.

Further, the present inventors have found that hydrogen gas is formedaccompanied to a reaction in these synthesis techniques, and sometimes aphenomenon happen to occur in which a large amount of hydrogen gas isformed in the reaction, and that various problems are caused by thisphenomenon. For example, scaling up of the synthesis reaction increasesan amount of hydrogen gas to be formed, and too much increase of anamount of hydrogen gas formed could lead to an impairment of sufficientassurance of safety in a production circumstances. Further, when such anembodiment is employed that distillation purification is carried outdirectly after completion of the reaction by a distillation purificationequipment installed to a reactor, reaction solution is blown even to thedistillate side together with the hydrogen gas spouted up, causinglowering in purification efficiency.

Thus, an object of the present invention is to provide a mean forproducing a high purity of borazine compound safely and in a high yield.

According to an aspect of the present invention, a method for producinga borazine compound having a step to prepare a) an alkali boron hydriderepresented by ABH₄ (A represents a lithium atom, a sodium atom or apotassium atom) and an amine salt represented by (RNH₃)_(n)X (Rrepresents a hydrogen atom or an alkyl group, X represents a sulfategroup or a halogen atom, and n is 1 or 2) with a water content nothigher than 1% by mass, or b) diborane (B₂H₆) and an amine representedby RNH₂ (R represents a hydrogen atom or an alkyl group) with a watercontent not higher than 1% by mass, and a step to synthesize a borazinecompound by reacting the alkali boron hydride and the amine salt, or thediborane and the amine in a solvent, is provided. By the method of thepresent aspect, a high purity of borazine compound with a lower contentof decomposed matter can be produced in a high yield.

According to another aspect of the present invention, a method forproducing a borazine compound having a step to prepare a) an alkaliboron hydride represented by ABH₄ (A represents a lithium atom, a sodiumatom or a potassium atom) and an amine salt represented by (RNH₃)_(n)X(R represents a hydrogen atom or an alkyl group, X represents a sulfategroup or a halogen atom, and n is 1 or 2), or b) diborane (B₂H₆) and anamine represented by RNH₂ (R represents a hydrogen atom or an alkylgroup), and a step to synthesize a borazine compound by reacting thealkali boron hydride and the amine salt, or the diborane and the aminein mixed solvents containing a first solvent having a boiling point notlower than the boiling point of the borazine compound+50° C. and asecond solvent having a boiling point not higher than the boiling pointof the borazine compound+30° C., is provided.

According to further another aspect of the present invention, a methodfor producing a borazine compound having a step to prepare a) an alkaliboron hydride represented by ABH₄ (A represents a lithium atom, a sodiumatom or a potassium atom) and an amine salt represented by (RNH₃)_(n)X(R represents a hydrogen atom or an alkyl group, X represents a sulfategroup or a halogen atom, and n is 1, or 2), or b) diborane (B₂H₆) and anamine represented by RNH₂ (R represents a hydrogen atom or an alkylgroup), and a step to synthesize a borazine compound by reacting thealkali boron hydride and the amine salt, or the diborane and the aminein a solvent by gradually feeding into a reactor at least one of i) thealkali boron hydride or the diborane, and ii) the amine salt or theamine, is provided. By the method of the present aspect, an amount ofhydrogen gas formed in producing a borazine compound is controlled, anda borazine compound can be produced safely and in a high yield.

According to further another aspect of the present invention, a methodfor producing a borazine compound having a step to prepare a) an alkaliboron hydride represented by ABH₄ (A represents a lithium atom, a sodiumatom or a potassium atom) and an amine salt represented by (RNH₃)_(n)X(R represents a hydrogen atom or an alkyl group, X represents a sulfategroup or a halogen atom, and n is 1, or 2), or b) diborane (B₂H₆) and anamine represented by RNH₂ (R represents a hydrogen atom or an alkylgroup), and a step to synthesize a borazine compound by reacting thealkali boron hydride and the amine salt, or the diborane and the aminein a solvent, while a solvent is fed to a cooling section of a synthesisapparatus, is provided. By the method of the present aspect, the problemthat a deposition is formed in a cooling section of a synthesisapparatus in synthesizing a borazine compound is effectively suppressed,and a borazine compound can be produced safely and in a high yield.

According to further another aspect of the present invention, a methodfor producing a purified N-alkylborazine having a step to purify bydistilling an N-alkylborazine and a step to remove a compound depositedin the N-alkylborazine by filtration. By the method of the presentaspect, a purified N-alkylborazine with a high purity can be obtained.

According to further another aspect of the present invention, anN-alkylborazine containing an N-alkylcycloborazane and a boron ethercompound in a total content not higher than 0.1% by mass is provided.

By these aspects, an N-alkylborazine containing a very low content of aboron ether compound can be obtained. As a result, characteristics of aninterlayer dielectric film and the like produced using anN-alkylborazine can be improved.

DETAILED DESCRIPTION OF THE INVENTION

In an aspect, the present invention relates to a method for producing aborazine compound. In the method of the present invention, a borazinecompound is synthesized by a reaction of an alkali boron hydriderepresented by ABH₄ (A represents a lithium atom, a sodium atom or apotassium atom) and an amine salt represented by (RNH₃)_(n)X (Rrepresents a hydrogen atom or an alkyl group, X represents a sulfategroup or a halogen atom, and n is 1 or 2) (hereinafter, also referred toas “reaction 1”), or a reaction of diborane (B₂H₆) and an aminerepresented by RNH₂ (R represents a hydrogen atom or an alkyl group)(hereinafter, also referred to as “reaction 2”). Here, in the presentapplication, “borazine” means borazine (B₃N₃H₆) in which none of boronatom nor nitrogen atom is bonded with an alkyl group, and “borazinecompound” means a borazine derivative in which at least one of nitrogenatom is bonded with an alkyl group.

Hereinbelow, the method of the present invention will be explained indetail.

Firstly, raw materials necessary for the reaction are prepared. In thereaction 1, an alkali boron hydride represented by ABH₄ (A represents alithium atom, a sodium atom or a potassium atom) and an amine saltrepresented by (RNH₃)_(n)X (R represents a hydrogen atom or an alkylgroup, X represents a sulfate group or a halogen atom, and n is 1 or 2)are prepared as raw materials.

In the alkali boron hydride (ABH₄), A represents a lithium atom, asodium atom or a potassium atom. Examples of the alkali boron hydrideinclude sodium boron hydride and lithium boron hydride.

In the amine salt ((RNH₃)_(n)X), R represents a hydrogen atom or analkyl group; X represents a sulfate group or a halogen atom; and n is 2when X is a sulfate group, and n is 1 when X is a halogen atom. Halogenatom is preferably a chlorine atom. When n is 2, R may be the same ordifferent from each other. In view of yield in the synthesis reactionand easiness in handling, R is preferably an alkyl group being same toeach other. The alkyl group may be straight chained, branched or cyclic.Number of carbon atom of the alkyl group is not especially limited, butpreferably 1 to 8 atoms, more preferably 1 to 4 atoms, and furthermorepreferably one atom. Specific examples of the alkyl group include, forexample, methyl group, ethyl group, propyl group, isopropyl group, butylgroup, isobutyl group, sec-butyl group, tert-butyl group, pentyl group,isopentyl group, neopentyl group, hexyl group, heptyl group, octylgroup, nonyl group, decyl group, cyclopropyl group, cyclopentyl groupand cyclohexyl group. An alkyl group other than these may be also used.Examples of the amine salt include ammonium chloride (NH₄Cl),monomethylamine hydrochloride (CH₃NH₃Cl), monoethylamine hydrochloride(CH₃CH₂NH₃Cl), monomethylamine hydrobromide (CH₃NH₃Br), monoethylaminehydrofluoride (CH₃CH₂NH₃F), ammonium sulfate ((NH₄)₂SO₄) andmonomethylamine sulfate ((CH₃NH₃)₂SO₄).

On the other hand, in the reaction 2, as raw materials of the reaction,diborane (B₂H₆) and an amine represented by RNH₂ (R represents ahydrogen atom or an alkyl group) are prepared.

Diborane is a compound represented by the chemical formula “B₂H₆”. Here,diborane may be a complexed one with tetrahydrofuran or the like.Further, regarding to the amine, R is same as explained for the aminesalt in the paragraph for raw materials of the reaction 1, and henceexplanation will be omitted here.

The raw materials to be used may be selected corresponding to astructure of a borazine compound to be synthesized. For example, whenN-trimethylborazine in which N atoms constructing a borazine ring arebonded with methyl groups is produced, an amine salt or an amine whereinR is a methyl group, such as monomethylamine hydrochloride as an aminesalt, and monomethylamine as an amine, may be used.

Method for obtaining raw materials is not especially limited. Each ofthe raw materials described above may be synthesized according to aknown technique, or used by purchasing a commercial product.

In an aspect of the present invention, as a raw material forsynthesizing a borazine compound, an amine salt (when a borazinecompound is synthesized by the reaction 1) or an amine (when a borazinecompound is synthesized by the reaction 2) with a low water content isused.

Specifically, in the present aspect, water content in the amine salt orthe amine as a raw material is not higher than 1% by mass, preferablynot higher than 0.1% by mass and more preferably not higher than 0.05%by mass. By synthesizing using the amine salt or the amine with such lowwater content, synthesis of a high purity of borazine compound becomespossible. Mechanism thereof is not clear, but it is speculated thatdecomposition of the synthesized borazine compound caused by mix-in ofwater is effectively inhibited. Further, when a borazine compound issynthesized by the reaction of diborane and an amine, if water contentof the amine is high, diborane rapidly reacts with water contained inthe amine to form boric acid. Contrary, according to the present aspect,occurrence of such problem can be also effectively suppressed. In thisconnection, as a value of water content in an amine salt or an amine asa raw material, a value measured by the method used in Examplesdescribed later will be employed. Further, from the above viewpoint, awater content of an amine salt or an amine is preferably as low aspossible. The lower limit of the water content is not especiallylimited, but a water content of an amine salt or an amine for practicaluse is preferably not lower than 10 ppm by mass.

Route to obtain an amine salt or an amine with lower water content isnot especially limited. When a commercial product of an amine salt or anamine with lower water content is available in the market, the productmay be purchased and used, or after purchasing a commercial product withcomparatively higher water content generally available in the market,the product may be used for synthesizing a borazine compound bypersonally reducing water content thereof.

Method for personally reducing water content of an amine salt or anamine is also not especially limited; a conventionally known knowledgein the field of chemical synthesis can be referred to, as appropriate.An example of the method for personally reducing water content of anamine salt or an amine includes, for example, heat drying, drying underreduced pressure and drying with desiccant (for example, silica gel andsodium sulfate). Among them, heat drying can be preferably employed. Inthis case, heating temperature is not especially limited, and atemperature as low as an amine salt or an amine is not decomposed and ashigh as drying time does not become too long, may be employed.Specifically, heating temperature in heat drying is preferably around 20to 150° C. and more preferably around 60 to 100° C. Too low temperaturein heat drying could require a long drying time. Contrary, too hightemperature in heat drying could require a long cooling time for takingout.

The treatment for reducing water content of an amine salt or an amine byheat drying is preferably conducted under reduced pressure. In thiscase, specific pressure condition is not especially limited, butpreferably around 0.0001 to 0.7 Pa and more preferably around 0.001 to0.1 Pa. Too low pressure in reducing pressure could lead to sublimationof a borazine compound. Contrary, too high pressure in reducing pressurecould require a long drying time.

In a preferable embodiment, water contents in other raw materials arealso controlled at low levels. By such embodiment, decomposition of aborazine compound due to contact with moisture and lowering in purityaccompanied thereto can be further suppressed.

Specifically, water content of an alkali boron hydride (when a borazinecompound is synthesized by the reaction 1) or diborane (when a borazinecompound is synthesized by the reaction 2) is preferably not higher than1% by mass, more preferably not higher than 0.5% by mass and furthermore preferably not higher than 0.1% by mass. In this connection, as avalue of water content of an alkali boron hydride or diborane, a valuemeasured by the method used in an Example described later will beemployed. Further, from the above viewpoint, a water content of analkali boron hydride or diborane is preferably as low as possible. Alower limit of the water content is not especially limited, but a watercontent of an alkali boron hydride or diborane for practical use ispreferably not lower than 10 ppm by mass.

Embodiments such as a route to obtain an alkali boron hydride ordiborane with lower water content and a method for personally reducingwater content are same as described above for an amine salt or an amine,hence explanation thereof will be omitted here.

In further another preferable embodiment, water content of a solventused for synthesis (will be described later) is also controlled at a lowlevel. By such embodiment, decomposition of a borazine compound due tocontact with moisture and lowering in purity accompanied thereto canalso be further suppressed.

Specifically water content of a solvent is preferably not higher than 1%by mass, more preferably not higher than 0.5% by mass and further morepreferably not higher than 0.1% by mass. In this connection, as a valueof water content of a solvent, a value measured by the method used in anExample described later will be employed. Further, from the aboveviewpoint, water content of a solvent is preferably as low as possible.A lower limit of the water content is not especially limited, but awater content of a solvent for practical use is preferably not lowerthan 10 ppm by mass.

Route to obtain a solvent with lower water content is not especiallylimited. When a commercial product of a solvent with lower water contentis available in the market, the product may be purchased and used, orafter purchasing a commercial product with comparatively higher watercontent generally available in the market, the product may be used forsynthesizing a borazine compound by personally reducing water contentthereof.

Method for personally reducing water content of a solvent is also notespecially limited, and a conventionally known knowledge in the field ofchemical synthesis can be referred to, as appropriate. An example of themethod for personally reducing water content of a solvent includes, forexample, such a method as distilling after adding desiccant.

Subsequently, a borazine compound is synthesized by reacting the rawmaterials prepared as described above in a solvent. In this case, amixing ratio of an alkali boron hydride and an amine salt when aborazine compound is synthesized by the reaction 1 is not especiallylimited, but an amount of alkali boron hydride to be used is preferably1.0 to 1.5 moles based on 1 mole of an amount of amine salt to be used.And also, a mixing ratio of diborane and an amine when a borazinecompound is synthesized by the reaction 2 is not especially limited, butan amount of diborane to be used is preferably 1.0 to 1.2 moles based on1 mole of an amount of amine to be used.

Solvent for synthesis is not especially limited, but includes, forexample, tetrahydrofuran, monoethylene glycol dimethyl ether(monoglyme), diethylene glycol dimethyl ether (diglyme), triethyleneglycol dimethyl ether (triglyme) and tetraethylene glycol dimethyl ether(tetraglyme).

In another aspect of the present invention, solvents of two or morekinds having different boiling points are used. Specifically, assolvents for synthesizing a borazine compound, a first solvent having aboiling point not lower than the boiling point of the borazine compoundto be synthesized+50° C. and a second solvent having a boiling point nothigher than the boiling point of the borazine compound to besynthesized+30° C. are used. In this connection, a boiling point of aborazine compound cannot be determined unambiguously, because it can bevaried depending on a type of substituent thereof. For example, aboiling point of N,N′,N″-trimethylborazine is 133° C./760 mmHg, and aboiling point of N,N′,N″-triethylborazine is 184° C./760 mmHg.

A volatile component of the first solvent having a boiling point notlower than the boiling point of the borazine compound+50° C. liquefiescomparatively rapidly on cooling in a cooling section of synthesisapparatus and returns to a heating section. And in the cooling section,a deposition represented by N-alkylcycloborazane is formed. On the otherhand, a volatile component of the second solvent does not liquefy untilreaching at a lower temperature. Thus, the second solvent liquefied bycooling passes through a site, where a deposition is formed, on a way toreturn to a heating section. On this occasion, the deposition is removedwith the second solvent.

This mechanism can easily be understood if a cooling tube used in alaboratory scale synthesis is imagined. The first solvent liquefies at alower part of the cooling tube and returns to a flask attached to thecooling tube. And in the lower part of the cooling tube,N-alkylcycloborazane deposits. On the other hand, the second solventliquefies at the upper part of the cooling tube. On the way of thesecond solvent to return to a flask, the second solvent passes through asite, where N-alkylcycloborazane deposits, and N-alkylcycloborazane iswashed away. However, the present invention is not limited to alaboratory scale of implementation. Even in an industrial scale ofsynthesis using a distillation column or the like, the present inventioncan be used.

As described above, in the present aspect, a first solvent having aboiling point not lower than the boiling point of the borazinecompound+50° C. and a second solvent having a boiling point not higherthan the boiling point of the borazine compound+30° C. are used,however, a third solvent may optionally be used. Further, as a firstsolvent and a second solvent, a plurality of solvents may be used.

The first solvent has a boiling point higher than the boiling point ofthe borazine compound to be synthesized by not lower than 50° C. Theboiling point of a borazine compound means the boiling point of theborazine compound as a desired substance of the synthesis. When two ormore kinds of borazine compounds are synthesized as desired substances,the boiling point of a borazine compound means a boiling point of aborazine compound having a higher boiling point. An upper limit of aboiling point of the first solvent is not especially limited, but sincetoo high boiling point makes a separation by distillation purificationdifficult, preferably a solvent having a boiling point not higher thanthe boiling point of the borazine compound+150° C. is used.

A solvent included in the category of the first solvent is differentdepending on a boiling point of a borazine compound to be synthesized.Specific examples which can be used as the first solvent include, forexample, tetrahydrofuran, monoethylene glycol dimethyl ether(monoglyme), diethylene glycol dimethyl ether (diglyme), triethyleneglycol dimethyl ether (triglyme) and tetraethylene glycol dimethyl ether(tetraglyme).

The second solvent has a boiling point not higher than the boiling pointof the borazine compound+30° C. Definition of the boiling point of aborazine compound is same as described above. A lower limit of a boilingpoint of the second solvent is not especially limited, but if theboiling point of the second solvent is close to a boiling point of aborazine compound as an objected substance, separation by distillationpurification becomes difficult. Thus, the boiling point of the secondsolvent is preferably not lower than the boiling point of the borazinecompound+10° C., or not higher than the boiling point of the borazinecompound−10° C.

A solvent included in the category of the second solvent is alsodifferent depending on a boiling point of a borazine compound to besynthesized. Specific examples, which can be used as the second solvent,include, for example, ethers such as tetrahydrofuran, monoethyleneglycol dimethyl ether (monoglyme), diethylene glycol dimethyl ether(diglyme), triethylene glycol dimethyl ether (triglyme) andtetraethylene glycol dimethyl ether (tetraglyme); aromatic hydrocarbonssuch as benzene, toluene, xylene, mesitylene, ethylbenzene,propylbenzene and isopropylbenzene; alicyclic hydrocarbons such ascyclohexane, tetralin and decalin.

In the present aspect, a mixing ratio of the first solvent and thesecond solvent is not especially limited, but for securing an effect towash away the deposit with the second solvent, an amount of the secondsolvent to be used is preferably 0.1 to 2 times (by volume) based on 1of an amount of the first solvent to be used.

The deposition formed in a cooling section of synthesis apparatus isremoved with the second solvent, but more complete removal of thedeposition may be intended. Even when deposition is compulsorily removedby stopping synthesis once, it is possible to prolong an interval ofmaintenance or reduce a maintenance work, because removal of thedeposition has been done with the second solvent.

In further another aspect of the present invention, when a borazinecompound is synthesized by reacting raw materials in a solvent, at leastone of i) an alkali boron hydride (in the case of the reaction 1) ordiborane (in the case of the reaction 2), and ii) an amine salt (in thecase of the reaction 1) or an amine (in the case of the reaction 2) isgradually fed into a reactor.

Conventionally, in the reaction 1 and the reaction 2, a method forproduction had been employed in which reaction is progressed by chargingboth compounds as solid into a reactor then feeding a solvent thereto.However, in this method, due to presence of a whole amount of rawmaterials in the reaction system, under some conditions, a large amountof reactants could react instantaneously and a large amount of hydrogengas could be instantaneously generated.

Therefore, in the present aspect, to prevent a large amount of hydrogengas to be generated by a reaction, at least one of i) an alkali boronhydride (in the case of the reaction 1) or diborane (in the case of thereaction 2), and ii) an amine salt (in the case of the reaction 1) or anamine (in the case of the reaction 2) is gradually fed into a reactor.By this method, an instantaneous generation of a large amount ofhydrogen gas is prevented. Hereinbelow, the reaction 1 will bespecifically explained as an example, but the reaction 2 is also similarthereto.

As an embodiment to feed an alkali boron hydride and an amine salt intoa reactor, the following three embodiments are exemplified. Firstly, anembodiment, in which a whole amount of an alkali boron hydride ischarged into a reactor, then an amine salt is gradually fed into thereactor, is exemplified (a first embodiment). Secondly, an embodiment,in which a whole amount of an amine salt is charged into a reactor, thenan alkali boron hydride is gradually fed into the reactor, isexemplified (a second embodiment). Thirdly, an embodiment, in which bothof an alkali boron hydride and an amine salt are gradually fed into thereactor, is exemplified (a third embodiment).

In any embodiment, an instantaneous generation of a large amount ofhydrogen gas is prevented, and various effects can be obtained. Forexample, since an amount of hydrogen gas to be generated can becontrolled even when reaction is scaled up, a high safety is ensured.Further, when an embodiment is employed, in which distillationpurification is carried out directly after completion of reaction byfitting a distillation purification equipment to a reactor, aphenomenon, that a reaction solution is blown to a distillate sidetogether with hydrogen gas spouted out to lower purification efficiency,can be suppressed.

In the present aspect, an embodiment to feed a solvent in synthesizing aborazine compound is not especially limited. In the first embodiment, anamine salt is fed into a reactor charged with a whole amount of analkali boron hydride, and a solvent may be fed into a reactor chargedwith an alkali boron hydride before feeding the amine salt. A solventmay be fed into a reactor in advance, and a solvent may be fed togetherwith feed of an amine salt. Further, when a solvent is fed together withfeed of an amine salt into a reactor, the amine salt may be fed afterdissolving or dispersing the amine salt in a solvent, or chargedseparately into a reactor.

In the second embodiment, an alkali boron hydride is fed into a reactorcharged with a whole amount of an amine salt, and a mode to feed asolvent is not especially limited similarly as in the first embodiment.

Also, in the third embodiment, a mode to feed a solvent is notespecially limited. A solution composed of an alkali boron hydride and asolvent and a solution composed of an amine salt and a solvent may beprepared in advance then fed into a reactor. Only one of an alkali boronhydride and an amine salt is mixed with a solvent, and the other may befed into a reactor as a solid. A solvent is fed into a reactor inadvance, after that, an alkali boron hydride and an amine salt may befed thereto.

In the present aspect, “gradually fed” is that a prescribed amount ofcomponent is fed in small portions instead of feeding in one portion.Feeding time may be determined corresponding to reaction scale and kindof compound to be used. For example, feeding is carried out over 0.5 to5 hours. Feeding of raw materials into a reactor may be continuously orintermittently. If an amount to be fed can be determined by an empiricalrule or an experiment, feeding may be controlled so that total amount tobe fed becomes the prescribed amount. Further, feeding of a solvent maybe done automatically or manually. For example, when production iscarried out in a laboratory scale, a solvent may be fed, as appropriate,while an amount of deposition is checked with eyes.

Temperature of a reaction solution in a reaction (the reaction 1 or thereaction 2) (hereinafter, also simply referred to as “reactiontemperature”) is not especially limited. Reaction temperature ispreferably 20 to 250° C., more preferably 50 to 240° C., furtherpreferably 50 to 220° C., further more preferably 70 to 150° C., stillfurther more preferably 80 to 130° C. and yet further more preferably100 to 120° C. When reaction is carried out at a temperature in therange, an amount of hydrogen gas to be generated can be easilycontrolled. Reaction temperature can be measured using a temperaturesensor such as a K type thermo couple.

In this connection, “reaction temperature” means a temperature when areaction (the reaction 1 or the reaction 2) proceeds. When an alkaliboron hydride and an alkylamine salt are reacted (in the case of thereaction 1), N-alkylborazine is thought finally synthesized via anintermediate. In this case, “reaction temperature” does not mean atemperature throughout the whole reaction, but a temperature whenreaction of an alkali boron hydride and an alkylamine salt proceeds.

Reaction temperature may be not constant, but varied during thereaction. For example, reaction temperature is controlled at a lowerlevel in an initial stage of reaction to prevent N-alkylcycloborazanefrom converting to N-alkylborazine. And after most part of raw materialsconverted to N-alkylcycloborazane, reaction temperature is raised up tocomplete a synthesis of N-alkylborazine. Thus, when an embodiment isemployed, in which after substantially completing the reaction of analkali boron hydride and an alkylamine salt, a temperature of reactionsolution is raised up to mature the reaction, the temperature until thereaction of an alkali boron hydride and an alkylamine salt issubstantially completed corresponds to “reaction temperature”.

A mechanism that an amount of hydrogen gas to be generated can becontrolled by controlling reaction temperature is not clear, but it ispresumed that a reaction in which N-alkylcycloborazane is converted toN-alkylborazine proceeds at a comparatively high temperature. Namely, inthe synthesis of N-alkylborazine, N-alkylborazine is presumed to beformed by a mechanism that N-alkylcycloborazane having a generalstructure represented by the formula below is formed in first as anintermediate, then hydrogen (3H₂) is removed from N-alkylcycloborazane.And this reaction is thought to proceed at a comparatively hightemperature. For this reason, by controlling reaction temperature in theabove-described temperature range, most part of the reactant can be oncestopped at a stage of N-alkylcycloborazane, thus preventing aninstantaneous formation of a large amount of hydrogen gas. In thisconnection, the mechanism is a mere presumption, a technical scope ofthe present invention is by no means limited by the mechanism.

On another aspect of the present invention, for a purpose to removedeposition formed in the cooling section of synthesis apparatus, asolvent is fed to the cooling section of synthesis apparatus in thesynthesis. In the viewpoint that deposition is washed away with asolvent, the present aspect is similar to the aspect using mixedsolvents described above. In the present aspect, deposition is washedaway by a solvent fed to the cooling section of synthesis apparatusinstead of using a solvent cooled and liquefied.

Specifically, in the synthesis, a solvent is fed to the cooling sectionof synthesis apparatus where deposition is accumulated. By feeding asolvent to a site where deposition is accumulated, accumulation ofdeposition in the cooling section is prevented. A solvent to be fed maybe the same to the solvent used for synthesis of a borazine compound, ora different solvent may be used. As a solvent to be fed, those compoundsexemplified above as a solvent to be used for synthesis can be similarlyused.

An amount of a solvent to be fed differs depending on a structure ofsynthesis apparatus and scale of synthesis, and hence it is difficult tobe unambiguously specified. Corresponding to a synthesis apparatus to beused, a sufficient amount of a solvent to remove deposition ispreferably fed. However, since too large amount of a solvent to be fedleads to increase in cost of chemicals and scale-up of a productionapparatus, an amount to be fed is preferably small.

Method for feeding a solvent is not especially limited as long asdeposition can be removed. For example, a solvent feeding apparatus isinstalled above the cooling section of synthesis apparatus, so thatnecessary amount of a solvent and necessary timing of feeding can becontrolled.

Feeding of a solvent may be continuous or intermittent. Further, feedingof a solvent may be automatic or manual. For example, when production iscarried out in a laboratory scale, a solvent is fed, as appropriate,while an amount of deposition is checked with eyes.

By feeding a solvent, deposition formed in the cooling section ofsynthesis apparatus is removed, but more complete removal of thedeposition may be intended. Even when deposition is compulsorily removedby stopping the synthesis once, it is possible to prolong an interval ofmaintenance or reduce a maintenance work, because removal of thedeposition has been done with a solvent fed.

A borazine compound is a compound represented by the following formula.

Wherein, R is the same as described for an amine salt in the paragraphfor raw material of reaction 1, hence explanation is omitted here. Anexample of the borazine compound include, for example, borazine,N,N′,N″-trimethylborazine, N,N′,N″-triethylborazine,N,N′,N″-tri(n-propyl)borazine, N,N′,N″-tri(iso-propyl)borazine,N,N′,N″-tri(n-butyl)borazine, N,N′,N″-tri(sec-butyl)borazine,N,N′,N″-tri(iso-butyl)borazine, N,N′,N″-tri(tert-butyl)borazine,N,N′,N″-tri(1-methylbutyl)borazine, N,N′,N″-tri(2-methylbutyl)borazine,N,N′,N″-tri(neo-pentyl)borazine,N,N′,N″-tri(1,2-dimethylpropyl)borazine,N,N′,N″-tri(1-ethylpropyl)borazine, N,N′,N″-tri(n-hexyl)borazine,N,N′,N″-tricyclohexylborazine, N,N′-dimethyl-N″-ethylborazine,N,N′-diethyl-N″-methylborazine, and N,N′-dimethyl-N″-propylborazine. Inthis connection, in view of stability such as water resistance of aborazine compound to be produced, a borazine compound is preferablyN-alkylborazine.

A borazine compound synthesized can be purified, if necessary. As amethod for purifying a borazine compound, for example, distillationpurification is used. Distillation purification is a purification methodto separate impurities through a work in which a liquid is heated togenerate a gas and the gas is liquefied by cooling. Prior to thedistillation purification, a treatment, which is general in the field ofan organic synthesis, may be carried out. For example, a reactionsolution is filtered and concentrated using an evaporator.

Size and type of the distillation purification equipment may be decidedcorresponding to circumstances and scale. For example, when a largeamount of borazine compound is treated, an industrial scale ofdistillation column can be used. When a small amount of borazinecompound is treated, distillation purification using a distillation tubecan be used. For example, as a specific example of the distillationequipment for treating a small amount of borazine compound, adistillation equipment of a three-necked flask equipped with a Liebigcondenser using a Claisen type connecting tube can be used. However, thetechnical scope of the present invention is by no means limited to anembodiment using such distillation equipment.

Distillation condition is not especially limited. Corresponding to adesired borazine compound, a technique such as an atmosphericdistillation and a reduced pressure distillation may be selected.Temperature and pressure in the distillation are also not especiallylimited, but distillation temperature is preferably 130 to 180° C., andmore preferably 140 to 160° C. Distillation pressure is preferably 0.6kPa to 1.0 kPa, and more preferably 0.8 kPa to 1.0 kPa.

Distillation purification may be carried out optionally two or moretimes. Impurities are reduced to a suitable level by performing thedistillation purification two or more times or using a multistagedistillation column.

Preferably, even in a distillation purification step, a solvent is fedto a cooling section of distillation purification equipment. By feedinga solvent, formation of deposition in a cooling section can besuppressed even in the distillation purification step similarly as in asynthesis step. By this, even in the distillation purificationequipment, blockage of the cooling section can be prevented, andpurification efficiency can be improved. Embodiment for feeding asolvent in the distillation purification step is not especially limited,and the embodiment for feeding a solvent in a synthesis step describedabove can be similarly employed.

Further another aspect of the present invention relates to a techniquefor preventing contamination of impurities (in particular, anN-alkylcycloborazane and a boron ether compound) into a product when anN-alkylborazine is produced. Specifically, an N-alkylborazine issubjected to distillation purification, followed by removal of compoundsdeposited in the N-alkylborazine by filtration.

Route to obtain a N-alkylborazine to be purified in the present aspectis not especially limited. A high purity of N-alkylborazine may beproduced by purchasing an N-alkylborazine available in the market, andpurifying the N-alkylborazine. Alternatively, an N-alkylborazine may beobtained by synthesis. Since a technique to obtain an N-alkylborazine bysynthesis is same as described above, explanation thereof is omittedhere.

After an N-alkylborazine is obtained, the N-alkylborazine is purified toremove an N-alkylcycloborazane and/or a boron ether compound containedin the N-alkylborazine. Although a path of N-alkylcycloborazaneformation is not clear, N-alkylcycloborazane is thought to be anintermediate to N-alkylborazine formation as described above.N-alkylborazine is formed by dehydrogenation of N-alkylcycloborazane,but a part of N-alkylcycloborazane is thought to remain. Further, by aminor component in raw materials, boron ether compound is formed.However, since this is s presumed mechanism, the technical scope of thepresent invention is by no means limited by N-alkylcycloborazane orboron ether compound formed by the mechanism.

As a method for producing purified N-alkylborazine, a combination ofdistillation purification and filtration is preferable. When a commonpurification method is used, sometimes concentrations of aN-alkylcycloborazane and a boron ether compound cannot be decreased toan acceptable level for use for semiconductor materials. However, bycombining distillation purification and filtration as in the presentaspect, an N-alkylcycloborazane and a boron ether compound can beremoved to very low concentrations.

In a purification step, firstly N-alkylborazine is purified bydistillation. Since specific embodiment of the distillation purificationis the same as described above, explanation thereof is omitted here.

When an N-alkylcycloborazane and/or a boron ether compound is depositedin N-alkylborazine, an N-alkylcycloborazane and/or a boron ethercompound deposited in N-alkylborazine is removed by filtration.Deposition of an N-alkylcycloborazane and/or a boron ether compound isformed when distillate is cooled down in a distillation purificationstep. If necessary, a process to cool distillate containingN-alkylcycloborazane may be specially added. When one of anN-alkylcycloborazane or a boron ether compound deposits, the compounddeposited is removed by filtration. Both compounds may be removed byfiltration. Though amounts of an N-alkylcycloborazane and/or a boronether compound to be removed by filtration has a limitation, a purifiedN-alkylborazine having very low content of an N-alkylcycloborazaneand/or a boron ether compound can be obtained by depositing aN-alkylcycloborazane and/or a boron ether compound in N-alkylborazineand removing them by filtration.

Filtration condition is not especially limited. Corresponding tocircumstances and scale, a technique such as atmospheric filtration,pressure filtration and reduced pressure filtration may be selected. Akind of filter paper is also not limited. And corresponding tocircumstances and scale, filter paper, filter plate, cartridge filter,and the like may be used. Further, a material of filter paper is alsonot limited, but in view of reactivity of a borazine compound to besynthesized, for example, filter paper made of polytetrafluoroethylene(PTFE) or glass fiber is preferably used. Pore size of filtrationmaterial may be determined corresponding to amount and size ofdeposition. Pore size of filtration material may be made smallerstepwise. Pore size of filtration material is preferably 0.8 to 0.05 μm,and more preferably 0.5 to 0.05 μm.

In purified N-alkylborazine provided by the present aspect, totalcontent of an N-alkylcycloborazane and a boron ether compound ispreferably not higher than 0.1% by mass, and more preferably not higherthan 0.01% by mass. In this connection, when two or more kinds ofN-alkylcycloborazane or boron ether compound are contained, “content”means the total including all of them. Content of a N-alkylcycloborazaneis preferably not higher than 0.05% by mass, and more preferably nothigher than 0.005% by mass. Also, content of a boron ether compound ispreferably not higher than 0.05% by mass, and more preferably not higherthan 0.005% by mass. The lower a content of a N-alkylcycloborazane and aboron ether compound in purified N-alkylborazine is, the more thepurified N-alkylborazine is suitable to an application requiring a highpurity such as an interlayer dielectric film for semiconductor.

Contents of an N-alkylcycloborazane and a boron ether compound inpurified N-alkylborazine can be calculated using a known analyzer suchas a gas chromatography. In this case, when a significant difference isseen among the values measured by different analyzers, a value obtainedusing the measuring method described in Examples is content in thepresent invention.

If a preferable purified N-alkylborazine is specified from the viewpointof purity, a purified N-alkylborazine obtained by distillationpurification and filtration has a purity of preferably not lower than99.9% by mass, more preferably not lower than 99.99% by mass and furthermore preferably not lower than 99.999% by mass. According to the presentaspect, such a high purity of purified N-alkylborazine can be produced,and by using the purified N-alkylborazine with a high purity, quality ofproducts such as semiconductor devices can be improved.

Several aspects of the present invention described above can be used incombination. For example, in a synthesis reaction of a borazinecompound, mixed solvents of the first solvent and the second solvent areused. And in a synthesis, the mixed solvents are fed to a coolingsection of synthesis apparatus. By such way, formation of deposition ina cooling section of synthesis apparatus can be effectively suppressed.

In a more preferably embodiment, following the synthesis step,distillation purification step is carried out. In further morepreferable embodiment, in the distillation purification step, the mixedsolvents of the first solvent and the second solvent are fed in acooling section of the distillation purification equipment. According tosuch an embodiment, formation of deposition in a cooling section issuppressed even in the distillation purification step, a borazinecompound can be produced extremely safely and in a high yield.

Further, all of the aspects of the present invention may be used incombination. Namely, a borazine compound may be produced by a method forproduction having a step to prepare a) an alkali boron hydriderepresented by ABH₄ (A represents a lithium atom, a sodium atom or apotassium atom) and an amine salt represented by (RNH₃)_(n)X (Rrepresents a hydrogen atom or an alkyl group, X represents a sulfategroup or a halogen atom, and n is 1 or 2) with a water content nothigher than 1% by mass, or b) diborane (B₂H₆) and an amine representedby RNH₂ (R represents a hydrogen atom or an alkyl group) with a watercontent not higher than 1% by mass, a step to prepare mixed solventscontaining a first solvent having a boiling point not lower than theboiling point of the borazine compound+50° C. and a second solventhaving a boiling point not higher than the boiling point of the borazinecompound+30° C., a step to synthesize a borazine compound by reactingthe alkali boron hydride and the amine salt, or the diborane and theamine in the mixed solvents by gradually feeding into a reactor at leastone of i) the alkali boron hydride or the diborane, and ii) the aminesalt or the amine, a step to purify by distilling the synthesizedborazine compound, and a step to remove a compound deposited in theborazine compound by filtration. According to such an aspect, a highpurity of boazine compound can be produced safely and in a high yield.

In this connection, without any limitation to the combination describedabove, an aspect, in which each aspect of the present invention isoptionally selected and combined, can also similarly be employed.

Use of a borazine compound is not especially limited, but the compoundcan be used to form a low dielectric constant film such as an interlayerdielectric film for semiconductor, a barrier metal layer and an etchstopper layer. In such case, a borazine compound may be used or acompound derived from a borazine compound by modification may be used. Apolymer obtained by polymerizing a borazine compound or a borazinecompound derivative may be used as a raw material for an interlayerdielectric film for semiconductor, a barrier metal layer or an etchstopper layer.

A polymer can be formed with a compound having a borazine ring skeletonas a monomer. Polymerization method and polymerization mode are notespecially limited. Polymerization method is selected depending on afunctional group bonded to a borazine ring. For example, when an aminogroup is bonded, a polymer can be synthesized by condensationpolymerization. When a vinyl group or a functional group containing avinyl group is bonded to a borazine ring, a polymer can be formed byradical polymerization using a polymerization initiator. A polymer maybe a homopolymer, or a copolymer containing two or more monomer units.Type of copolymer may be any of a random copolymer, a block copolymer, agraft copolymer, and the like. By using a monomer having three or morefunctional groups which can form a bond with other monomer, a polymer inwhich monomers are bonded together like a network can be obtained.

Next, a method for forming an interlayer dielectric film forsemiconductor, a barrier metal layer or an etch stopper layer will beexplained. In this connection, in the following description, “a borazinecompound”, “a borazine compound derivative” and “a polymer originatedwith them” are referred to as “a borazine-ring-containing compound”.

To form an interlayer dielectric film for semiconductor, a barrier metallayer or an etch stopper layer using a borazine-ring-containingcompound, a technique to form a coating film by preparing a compositionin a solution state or a slurry state containing theborazine-ring-containing compound, and coating this composition. Asolvent used in such a case for dissolving or dispersing theborazine-ring-containing compound is not especially limited as long asthe solvent can dissolve or disperse the borazine-ring-containingcompound or other component to be added, if necessary. As the solvent,for example, alcohols such as ethylene glycol and ethylene glycolmonomethyl ether; aromatic hydrocarbons such as toluene, benzene andxylene; hydrocarbons such as hexane, heptane and octane;tetrahydrofurane; diglyme; and tetraglyme, are used. These solvents maybe used alone or in combination of two or more kinds. When filmformation is performed using spin coating, diglyme is preferably used.By using diglyme or a derivative thereof as a solvent, a uniformity of afilm to be produced is improved, and clouding of a film can beprevented. An amount of a solvent to be used for dissolving ordispersing the borazine-ring-containing compound is not especiallylimited, and may be determined corresponding to a production means forproducing a low dielectric constant material. For example, when filmformation is performed using spin coating, a kind and an amount of asolvent may be determined so that a viscosity becomes suitable for spincoating.

A composition containing the borazine-ring-containing compound isprovided to a desired site, dried and solidified. For example, to forman interlayer dielectric film for semiconductor, the composition may becoated on a substrate by spin coating, and dried. When a film having adesired thickness cannot be obtained in one coating and drying, coatingand drying may be repeated until a desired thickness is obtained. Filmforming conditions such as number of revolutions of spin coater, dryingtemperature and drying time are not especially limited.

Coating on a substrate may be performed using a technique other than thespin coating. For example, spray coating and dip coating can be used.

After that, a coating film is dried. Drying temperature of a coatingfilm is usually around 100 to 250° C. The “drying temperature” heremeans the highest temperature while drying treatment is carried out. Forexample, when a drying temperature is raised slowly, maintained at 10°C. for 30 min., and followed by cooling, a drying temperature is 100° C.Drying temperature can be measured using a thermo couple. Drying timefor coating film is not especially limited, but may be determined, asappropriate, in consideration of characteristics such as dielectricconstant and moisture resistance of a low dielectric constant materialto be obtained.

EXAMPLES

Hereinbelow, embodiments of the present invention will be explained indetail using Examples and Comparative Examples, however, technical scopeof the present invention is by no means limited to the followingembodiments.

In the following Example 1 and Comparative Example 1, water contents ofan amine salt and an alkali boron hydride as raw materials, as well assolvents were measured by the following techniques.

Namely, water contents of an amine salt and solvents were measured usingthe Karl Fischer AQ-7 (from Hiranuma Sangyo Co., Ltd.). In this case,Aqualyte RS as generator electrolyte and Aqualyte CN as counterelectrolyte were used.

And water content of an alkali boron hydride was measured using the KarlFischer CA-100 (from Mitsubishi Chemical Corp.). In this case,Aquamicron AX as generation liquid and Aquamicron CXU as counterelectrode liquid were used.

Further, purity of a borazine compound was measured using a gaschromatography. Measuring conditions were as follows.

Equipment: GC-14B from Shimadzu Corp.

Column: Ultra Alloy (8H) from Hitachi Science Systems Ltd.

Carrier gas: Nitrogen

Flow rate of carrier gas: 3.0 mL/min.

Sample injection temperature: 300° C.

Detector temperature: 300° C.

Sample injection amount: 0.2 μL

Column temperature: 50° C. (5 min.)→raising temperature to 250° C. at atemperature raising rate of 20° C./min.→raising temperature to 300° C.at a temperature raising rate of 10° C./min.→300° C. (10 min.)

Example 1

Firstly, as an amine salt of raw material of reaction, methylaminehydrochloride was prepared. Then, this methylamine hydrochloride wassubjected to heat drying under reduced pressure by standing under theatmosphere of 80° C., 0.07 MPa for 12 hours.

Similarly, as an alkali boron hydride of another raw material ofreaction, sodium boron hydride was prepared. This sodium boron hydridewas subjected to drying under reduced pressure by standing in theatmosphere of 25° C., 0.07 MPa for 12 hours.

On the other hand, as a solvent, triglyme was prepared. And by addingMolecular Sieve 3A (from Tomoe Engineering Co., Ltd.), this triglyme wasdried.

Into a reactor equipped with a condenser, methylamine hydrochloridedried as described above (33.5 g; water content=200 ppm by mass) andtriglyme dried as described above (98.6 g; water content=130 ppm bymass) were charged with nitrogen purge, then temperature of the reactionsystem was raised to 100° C.

On the other hand, sodium boron hydride dried as described above (21.0g; water content=300 ppm by mass) was prepared, then added into triglymedried as described above (88.7 g; water content=130 ppm by mass)prepared separately, to prepare a slurry.

The slurry of sodium boron hydride prepared as described above wasslowly added over 1 hour to the reactor raised to 100° C. as describedabove.

After completion of addition of the slurry, the reaction system wasraised to 200° C. over 2 hours, and further matured at 200° C. for 2hours to synthesize N,N′,N″-trimethylborazine.

The N,N′,N″-trimethylborazine thus obtained was distilled at 150 to 220°C. to obtain 15.4 g of purified N,N′,N″-trimethylborazine. Purity of thepurified N,N′,N″-trimethylborazine obtained was measured and found to be99.8% by mass.

Comparative Example 1-1

Into a reactor equipped with a condenser, methylamine hydrochloride notdried (33.5 g; water content 1.3% by mass) and triglyme not dried (98.6g; water content=2.0% by mass) were charged with nitrogen purge, thentemperature of the reaction system was raised to 100° C.

On the other hand, sodium boron hydride not dried (21.0 g; watercontent=2.0% by mass) was prepared, then added into triglyme not dried(88.7 g; water content=2.0% by mass) prepared separately, to prepare aslurry.

The slurry of sodium boron hydride prepared as described above wasslowly added over 1 hour to the reactor raised to 100° C. as describedabove.

After completion of addition of the slurry, the reaction system wasraised to 200° C. over 2 hours, and further matured at 200° C. for 2hours to synthesize N,N′,N″-trimethylborazine.

The N,N′,N″-trimethylborazine thus obtained was distilled at 150 to 220°C. to obtain 1.5 g of purified N,N′,N″-trimethylborazine. Purity of thepurified N,N′,N″-trimethylborazine obtained was measured and found to be93.5% by mass.

Comparative Example 1-2

Into a reactor equipped with a condenser, methylamine hydrochloride notdried (33.5 g; water content=2.0% by mass) and triglyme dried asdescribed above (98.6 g; water content=250 ppm by mass) were chargedwith nitrogen purge, then temperature of the reaction system was raisedto 100° C.

On the other hand, sodium boron hydride dried as described above (21.0g; water content=400 ppm by mass) was prepared, then added into triglymedried as described above (88.7 g; water content=250 ppm by mass)prepared separately, to prepare a slurry.

The slurry of sodium boron hydride prepared as described above wasslowly added over 1 hour to the reactor raised to 100° C. as describedabove.

After completion of addition of the slurry, the reaction system wasraised to 200° C. over 2 hours, and further matured at 200° C. for 2hours to synthesize N,N′,N″-trimethylborazine.

The N,N′,N″-trimethylborazine thus obtained was distilled at 150 to 220°C. to obtain 8.7 g of purified N,N′,N″-trimethylborazine. Purity of thepurified N,N′,N″-trimethylborazine obtained was measured and found to be97.4% by mass.

From the results of Example 1 and Comparative Examples 1-1 and 1-2, itis shown that by controlling water content of an amine salt as a rawmaterial of borazine compound at a low level, purity and yield ofborazine compound to be synthesized can be improved. Further, it is alsoshown that by controlling water contents of an alkali boron hydrate as araw material of borazine compound and a solvent used for synthesis at alow level, purity and yield of borazine compound to be synthesized canbe further more improved.

Example 2-1

Into a 4 L reactor equipped with a cooling tube, methylaminehydrochloride (335 g) as an amine salt, tetraglyme (boiling point: 275°C.) (500 g) as a first solvent, and diglyme (boiling point: 162° C.)(500 g) as a second solvent were charged, then temperature of thereaction system was raised to 100° C.

On the other hand, sodium boron hydride (210 g) as an alkali boronhydride was prepared, then added into tetraglyme (1,000 g) preparedseparately, to prepare a slurry.

The slurry of sodium boron hydride prepared as described above wasslowly added over 90 min. to the reactor raised to 100° C. as describedabove.

After completion of addition of the slurry, the reaction system wasraised to 200° C. over 30 min., and further matured at 200° C. for 2hours to proceed a synthesis reaction of N,N′,N″-trimethylborazine.

During raising temperature and maturing, formation of deposition andblockage of the cooling tube were observed by eyes, and it was foundthat the cooling tube was not blocked up though formation of thedeposition was observed a little.

Example 2-2

Into a 4 L reactor equipped with a cooling tube having a solventdropping device connected to the upper part thereof, methylaminehydrochloride (335 g) as an amine salt, triglyme (boiling point: 216°C.) (1,000 g) as a solvent were charged, then temperature of thereaction system was raised to 100° C.

On the other hand, sodium boron hydride (210 g) as an alkali boronhydride was prepared, then added into triglyme (1,000 g) preparedseparately, to prepare a slurry.

The slurry of sodium boron hydride prepared as described above wasslowly added over 90 min. to the reactor raised to 100° C. as describedabove.

After completion of addition of the slurry, the reaction system wasraised to 200° C. over 30 min., and further matured at 200° C. for 2hours to proceed a synthesis reaction of N,N′,N″-trimethylborazine.

In this case, 20 g each of triglyme was dropped from the solventdropping device 3 times in total during a period from completion ofaddition of the slurry until completion of raising temperature of thereaction system.

During raising temperature and maturing, formation of deposition andblockage of the cooling tube were observed by eyes, and it was foundthat though formation of the deposition was observed a little, thisdeposition was washed away by the dropped triglyme and the cooling tubewas not blocked up.

Comparative Example 2

Into a 4 L reactor equipped with a cooling tube, methylaminehydrochloride (335 g) as an amine salt, and tetraglyme (boiling point:275° C.) (1,000 g) were charged, then temperature of the reaction systemwas raised to 100° C.

On the other hand, sodium boron hydride (210 g) as an alkali boronhydride was prepared, then added into tetraglyme (1,000 g) preparedseparately, to prepare a slurry.

The slurry of sodium boron hydride prepared as described above wasslowly added over 90 min. to the reactor raised to 100° C. as describedabove.

After completion of addition of the slurry, the reaction system wasraised to 200° C., and further matured at 200° C. to proceed a synthesisreaction of N,N′,N″-trimethylborazine.

However, during the maturation, a deposition was formed inside of thecooling tube resulting in blockage of the cooling tube. For this reason,the reaction system was cooled down to stop progression of the reaction.

From the results shown in Example 2-1 and 2-2 and Comparative Example 2,it can be understood that by using a prescribed mixed solvents insynthesis of a borazine compound, or by feeding a solvent to a coolingsection of synthesis apparatus during synthesis, formation of depositionin a cooling section is suppressed. Because of formation of depositionin a cooling section being suppressed, blockage of the cooling sectioncan be prevented, and safe synthesis in a high yield becomes possible.

Example 3-1

Into a reactor equipped with a cooling tube, 12.1 g of lithium boronhydride as an alkali boron hydride and 187.3 g of tetraglyme as asolvent were charged with nitrogen purge, then temperature was raised to130° C. While the reaction solution was maintained at 130° C., 40.5 g ofethylamine hydrochloride as an alkylamine salt was fed over 1 hour toproceed the reaction of the alkali boron hydride and the alkylaminesalt. After that, temperature of the reaction solution was raised to200° C., and further matured at 200° C. for 2 hours. In this reactionprocess, a bumping phenomenon of the reaction solution was not observed.

Example 3-2

Into a reactor equipped with a cooling tube, 33.5 g of methylaminehydrochloride as an alkylamine salt and 98.6 g of triglyme as a solventwere charged with nitrogen purge, then temperature was raised to 100° C.While the reaction solution was maintained at 100° C., a mixed liquidcontaining 21.0 g of sodium boron hydride as an alkali boron hydride and88.7 g of triglyme as a solvent was fed over 1 hour to proceed thereaction of the alkali boron hydride and the alkylamine salt. Afterthat, temperature of the reaction solution was raised to 200° C., andfurther matured at 200° C. for 2 hours. In this reaction process, abumping phenomenon of the reaction solution was not observed.

Example 3-3

Into a reactor equipped with a cooling tube, 32.0 g of tetraglyme as asolvent was charged with nitrogen purge, and temperature was raised to70° C. While the reaction solution was maintained at 70° C., a mixedliquid containing 21.0 g of sodium boron hydride as an alkali boronhydride and 88.7 g of tetraglyme as a solvent, and a mixed liquidcontaining 33.5 g of ethylamine hydrochloride as an alkylamine salt and67.6 g of tetraglyme as a solvent were fed over 1 hour. After that, thereaction solution was raised to 200° C. over 2 hours, and furthermatured at 200° C. for 2 hours. In this reaction process, a bumpingphenomenon was not observed.

Comparative Example 3-1

Into a reactor equipped with a cooling tube, 21.0 g of sodium boronhydride as an alkali boron hydride and 33.5 g of methylaminehydrochloride as an alkylamine salt were charged with nitrogen purge.Further, 187.3 g of tetraglyme as a solvent was fed. After that, thereaction solution was raised to 100° C. over 1 hour, however, since abumping phenomenon of the reaction solution was observed, the reactionsolution was cooled down to stop the reaction. Bumping Temperaturephenomenon Synthesis of reaction in reaction process solution solutionExample 3-1 To (AB₄H + solvent) 130° C. No RNH₃X was fed ↓ 200° C.Example 3-2 To (RNH₃X + solvent) 100° C. No (AB₄H + solvent) was fed ↓200° C. Example 3-3 To solvent  70° C. No (RNH₃X + solvent) and ↓(AB₄H + solvent) were fed 200° C. Comparative To (AB₄H + RNH₃X) Reactionwas Yes Example 3 solvent was fed stopped at 100° C.

As described above, by the present invention, it is possible to controla reaction between an alkali boron hydride and an alkylamine salt, andan instantaneous generation of a large amount of hydrogen gas can beprevented.

Example 4 Synthesis Example

Into a 4 L reactor equipped with a condenser, 335 g of methylaminehydrochloride as an alkylamine salt and 1,000 g of triglyme as a solventwere charged with nitrogen purge, and temperature was raised to 100° C.After raising temperature, a slurry prepared by adding 210 g of sodiumboron hydride as an alkali boron hydride to 1,000 g of triglyme wasadded over 90 min. After addition of the slurry, the reaction solutionwas raised to 200° C. and further matured for 2 hours to formN,N′,N″-trimethylborazine (hereinafter, also referred to as “TMB”).After maturation, the condenser was removed, and a Claisen connectingtube and a Liebig cooling tube were fitted up, thenN,N′,N″-trimethylborazine was distilled off.

Into a 500 ml flask equipped with a Claisen connecting tube and a Liebigcooling tube, 150 g of N,N′,N″-trimethylborazine obtained in theSynthesis Example was charged, then distillation was conducted under theatmospheric pressure at a distilling temperature in a range of 155 to160° C., and a fraction at a distilling temperature of 130 to 133° C.was batched off. The distillate thus batched off was purified again bythe similar atmospheric distillation.

After the distillation purification, the distillate was filtered underreduced pressure using a 0.45 μm PTFE membrane filter. The filtrate wasanalyzed by a gas chromatography (Shimadzu Corp., GC-14B, column:Hitachi Science Systems Ltd., UltraALLOY(8H)), to find out 0.02% by massof boron ether compound as a component other thanN,N′,N″-trimethylborazine. An amount of N-alkylcycloborazane was belowthe detection limit.

Comparative Example 4

TMB obtained in the Synthesis Example was analyzed by a gaschromatography (Shimadzu Corp., GC-14B, column: Hitachi Science SystemsLtd., UltraALLOY(8H)), to find out 0.2% by mass of N-alkylcycloborazaneand 0.2% by mass of boron ether compound as a component other thanN,N′,N″-trimethylborazine. Total content of PurificationN-alkylcycloborazane and Process boron ether compound Example 4Distillation purification + 0.02% by mass Filtration ComparativeDistillation purification  0.4% by mass Example 4 only

As shown in the table, it is understood that by applying filtrationafter distillation purification, impurities contained in N-alkylborazinecan be effectively removed.

The present application is based on Japanese Patent Application No.2005-028068 filed on Feb. 3, 2005, Japanese Patent Application No.2005-030598 filed on Feb. 7, 2005, Japanese Patent Application No.2005-151501 filed on May 24, 2005, and Japanese Patent Application No.2005-242733 filed on Aug. 24, 2005, and the disclosures are incorporatedherein by reference in entirety.

1.-13. (canceled)
 14. A method for producing a purified N-alkylborazinecompound comprising: a step of distillation purification of anN-alkylborazine compound; and a step to remove a compound deposited inthe N-alkylborazine by filtration.
 15. A method according to claim 14,wherein a purity of the purified N-alkylborazine is not lower than 99.9%by mass.
 16. A method according to claim 14, wherein N-alkylborazine issynthesized by a reaction of a) an alkali boron hydride represented byABH₄ (A represents lithium atom, sodium atom or potassium atom) and anamine salt represented by (RNH₃)_(n)X (R represents hydrogen atom oralkyl group, X represents sulfate group or halogen atom, and n is 1, or2), or b) diborane (B₂H₆) and an amine represented by RNH₂ (R representshydrogen atom or alkyl group).
 17. N-alkylborazine containingN-alkylcycloborazane and boron ether compound in total amount not higherthan 0.1% by mass.
 18. (canceled)